i) 



CONSERVATION OF SKELETAL CALCIUM ATOMS THKOlfiH LIFE 221 



bone tissue. This great heterogeneity of the specific activity of the bone 

 apatite phosphorus could be demonstrated by Zetterstrom and Ljung- 

 (iREN*^^^^' by isohiting bone fractions of different solul)iHty and measuring 

 Hieir specific^ activity. The most soluble bone phosphorus was found 

 lo show the highest specific activity, thus the most rapid rate of renewal. 

 X-ray absorption and diffraction studies by Amprino and Engstrom*^' 

 revealed also thai the distril)ution of mineral components in the bone 

 1 issu(^ is far from being uniform. 



SIZE OF THE NON- RENEW ABLE PART OF THE SKELETON 



The extent of renewal of apatite phosphate of the skeleton can be 

 calculated from the mean value of the specific activity of the plasma 

 l)hosphate during the experiment and the value of the specific activity 

 of the apatite phosphate at the end of the experiment. During the ear]3^ 

 part of the experiment, the sensitivity of the radioactive indicator is 

 comparatively low, thus a strong decline in the plasma activity corres- 

 ponds to a comparatively low interchange figure. In the later part of 

 the experiment, the same activity which indicated at the start the pre- 

 sence of 1 mgm of phosphorus in the plasma, for example, indicates 

 100 mgm, thus the sensitivity of the radioactive indicator is strongly 

 increased. Now, a further interchange will be indicated by a very small 

 further loss of activity. Furthermore, following the interchange of 

 l)lasma and bone phosphate for a longer time interval, increase and 

 decrease in the specific activity of the plasma phosphate may alternate 

 due to a variation in the phosphate intake or other reasons. Thus, it 

 encounters difficulties, by comparing the mean specific activity 

 of the plasma phosphate during the experiment and the specific activity 

 of the apatite phosphate at the end of the experiment, to find a reliable 

 value for the extent of the renewable part of the mineral phosphate 

 of the skeleton, and similar considerations apply to the determinatior 

 of the renewable part of bone calcium in contrast to that of the bone 

 sodium. Sodium, being mainly an extracellular element, is distributed 

 between plasma and extracellular fluid within a few minutes, a distri- 

 bution wdiich results in a decrease in the specific activity of plasma 

 sodium to about i/g of its original value, followed by a slow decrease 

 with time only. Thus, as discussed on p. 16, the extent of the renewable 

 part of the mineral bone sodium could be calculated from specific acti- 

 \'\\y data. We can, however, determine the extent of renewal of bone 

 phosphate from specific activity data when keeping the specific activity 

 of the plasma phosphate at a constant level during the experiment. 

 This result was oblainerl bv the author and his associatrs^i by daily 



